This invention relates generally to information retrieval from an optically readable storage medium and, more specifically, to a new and improved method and apparatus for retrieving information from video discs and the like in a rapid and reliable manner.
Video disc players and the like are known for recovering information that has been stored, for instance, as a succession of light reflective and non-reflective regions along spirally-formed information tracks in a disc-shaped record carrier. The record carrier can be rotated at a relatively high rate, while an optical system is employed for directing a radiant beam, such as a laser beam, to impinge upon the information tracks and for gathering a reflected beam that has been modulated by the refective and non-reflective regions of the information track. Such a player includes a carriage for translating the video disc relative to the radiant beam at a rate equal to the pitch of the spirally-recorded tracks and beam steering means for manipulating the radiant beam to precisely follow the path defined by such tracks.
A frequency modulated electrical signal is recovered from the reflected, light modulated beam and is applied to appropriate signal processing circuitry for deriving a video signal for display on a video monitor. Various control signals that are utilized to operate the player are also derived from the reflected beam.
Heretofore, the capability has existed of displaying a selected frame of video information by prescribing the address of the frame or information track wherein it is stored, and causing the carriage to translate in a rapid manner to the vicinity of such information track. The address information has been specially encoded in both of the vertical blanking intervals present in each revolution of an information track comprising the two standard fields of a video frame.
More particularly, in order to retrieve the selected frame or information track, the carriage has been translated at a uniform rate, greater than the normal play speed of the player, towards such information track. During the course of translating the carriage, track addresses of at least some of the tracks crossed were detected, although it is obviously not possible to detect every track address in such a mode of operation. As soon as it was detected that the selected information track had been reached or crossed, the drive signal to the carriage was terminated. Invariably, however, the carriage travelled past the location of the selected track and it was at least necessary to drive the carriage once in the opposite direction to return to it.
By this prior technique, it was determined to always approach the selected information track from one direction when preparing to actually stop the carriage at the track. In other words, if the carriage were driven initially in the normal forward direction for retrieval, after overshooting the selected track the carriage would be driven in the reverse direction past the selected track again. Upon passing the track, the reverse drive signal would be terminated and the carriage would again overshoot. Finally, the normal play mode of the video disc player would be utilized to simply play into and stop at the selected information track.
If the selected track was reached in such a search mode by rapidly translating the carriage in the reverse direction, the carriage drive signal would be terminated upon reaching or passing the selected track, with the accompanying overshoot. From this position the video disc player utilized the normal play mode to play into and stop at the selected track, since the carriage was then located on the proper side for approaching the selected track.
It will be apparent that the aforedescribed techniques for recovering the information stored in selected tracks were prone to deficiencies. For instance, overshoot when approaching the selected track from either the forward or the reverse direction resulted in delays in retrieving the information stored on the track. The requirement of always approaching the selected track from one direction compounded the delay.
Hence, there has been a need for an improved, rapid information retrieval technique for use with video disc players and the like, wherein information is optically recovered by means of a radiant beam being impinged upon an information storage medium, that solves the aforedescribed problems. The present invention fulfills this need.